Metagenesis is the phenomenon in which one generation of certain plants and animals reproduce asexually, followed by the sexually reproducing generation. Both the forms are diploid in metagenesis hence, it is the false alternation of generation. Coelenterates exhibits metagenesis (e.g., Obelia) where polyp form alternates with medusa in its life cycle.

Feathers are the epidermal growth that forms distinctive outer covering or plumage in birds.

Feathers play a variety of roles like

(i) They help in creating airfoil shape for wings so, as to provide lift and help in flight.

(ii) Feathers helps in maintaining body temperature.

(iii) Feathers play a vital role in mating by providing secondary sex characters in both the sexes the colour and markings determine the attractiveness of mate.

Class-Cyclostomata is comprised of, the living jawless fishes. Their mouth is circular and lack jaws, hence they are also called agnathans. It works like a sucker and is surrounded by tentacles (e.g., lampreys and haglish). These also prosses rectroctable horny teeth.

Fishes possess dermal scales, each scale made of dentine that is secreted by dermal papilla. Placoid scales are hard and microscopic in size, their body is made up of dentine and exposed surface is covered with enamel, Cycloid scales are strong and extremely flexible.

They are large, oval and made up of isopectine (layer of collagenous fibre). Placoid Scales are the characteristic features of cartilaginous fishes. (e.g., Scoliodon). Whereas, cycloid scale are found in bony fishes (e.g., Catla catla).

There are certain characters acquired by reptiles for the terrestrial adaptations. Two of then are

(i) Their body is covered by dry and cornified skin and epidermal scales or scutes.

(ii) Fertilisation is internal.